This module takes the existing File::Glob module as a starting point and extends it to allow new filenames to be derived from the files matched by File::Glob.

This can be useful when carrying out batch operations on multiple files that have both an input filename and output filename and the output file can be derived from the input filename. Examples of operations where this can be useful include, file renaming, file copying and file compression.

To help explain what File::GlobMapper does, consider what code you would write if you wanted to rename all files in the current directory that ended in .tar.gz to .tgz. So say these files are in the current directory

alpha.tar.gz
beta.tar.gz
gamma.tar.gz

and they need renamed to this

alpha.tgz
beta.tgz
gamma.tgz

Below is a possible implementation of a script to carry out the rename (error cases have been omitted)

Notice that a file glob pattern *.tar.gz was used to match the .tar.gz files, then a fairly similar regular expression was used in the substitute to allow the new filename to be created.

Given that the file glob is just a cut-down regular expression and that it has already done a lot of the hard work in pattern matching the filenames, wouldn't it be handy to be able to use the patterns in the fileglob to drive the new filename?

Behind the scenes the globmap function does a combination of a file glob to match existing filenames followed by a substitute to create the new filenames.

Notice how both parameters to globmap are strings that are delimited by <>. This is done to make them look more like file globs - it is just syntactic sugar, but it can be handy when you want the strings to be visually distinctive. The enclosing <> are optional, so you don't have to use them - in fact the first thing globmap will do is remove these delimiters if they are present.

The first parameter to globmap, *.tar.gz, is an Input File Glob. Once the enclosing "< ... >" is removed, this is passed (more or less) unchanged to File::Glob to carry out a file match.

Next the fileglob *.tar.gz is transformed behind the scenes into a full Perl regular expression, with the additional step of wrapping each transformed wildcard metacharacter sequence in parenthesis.

In this case the input fileglob *.tar.gz will be transformed into this Perl regular expression

([^/]*)\.tar\.gz

Wrapping with parenthesis allows the wildcard parts of the Input File Glob to be referenced by the second parameter to globmap, #1.tgz, the Output File Glob. This parameter operates just like the replacement part of a substitute command. The difference is that the #1 syntax is used to reference sub-patterns matched in the input fileglob, rather than the $1 syntax that is used with perl regular expressions. In this case #1 is used to refer to the text matched by the * in the Input File Glob. This makes it easier to use this module where the parameters to globmap are typed at the command line.

The final step involves passing each filename matched by the *.tar.gz file glob through the derived Perl regular expression in turn and expanding the output fileglob using it.

The end result of all this is a list of pairs of filenames. By default that is what is returned by globmap. In this example the data structure returned will look like this

File::GlobMapper has been kept simple deliberately, so it isn't intended to solve all filename mapping operations. Under the hood File::Glob (or for older versions of Perl, File::BSDGlob) is used to match the files, so you will never have the flexibility of full Perl regular expression.